During the production of semiconductor dice or chips, many semiconductor dice are formed together on a single wafer. The wafer is then cut to separate the individual dice. Each of these semiconductor dice should then be individually mounted onto a support surface for further processing by utilizing a die bonding process. Thereafter, electrical connections are created between the dice and external devices, and the dice are later encapsulated with a plastic compound to protect them from the environment.
In prior art die bonders utilized in the said die bonding process, each individual die is usually picked up by a bond arm from the wafer and then transported to a substrate to perform attachment of the die onto the substrate. A die bonder generally comprises a die bond head which has an air nozzle for creating a suction force to pick up a semiconductor die from a wafer platform holding the die. The die is then transported and bonded onto a substrate.
In order to place the die correctly and accurately onto the substrate, visual alignment is conducted with a vision system to capture images of the die on the wafer platform and the substrate. Positioning of the bond head and air nozzle will be performed according to the image captured of the die, which references an alignment pattern or fiducial mark on the die for this purpose. The bond head uses the captured image of the die to perform rotary compensation along a theta axis after picking up the die. Next, the bond head rotates and aligns the die to the orientation of the substrate before moving downwards to perform bonding. Downward movement of the bond head is facilitated by a z-axis motion motor while a bond force actuator applies a compressive force to the die directly. The compressive bonding force must be sufficiently large for pressing the die to the substrate.
FIG. 1 is a side view of a conventional die bonder 100 incorporating a preloaded compression spring 102 for die bonding. A bond head 101 of the die bonder 100 is mounted to a bond head mount 103, which is further slidably supported by a z-axis motion table 106. The bond head 101 applies a large bonding force on a die 108 during bonding aided by the preloaded compression spring 102. Additionally, there is a rotary motor 104 which is operative to rotate the bond head 101 for rotary or theta motion compensation.
When the z-axis motion table 106 moves downwards, it compresses the compression spring 102 and increases the bonding force acting on a die 108 after the die 108 contacts a substrate 110. A large z-axis drive-in motion in the vertical direction is created which induces an X-Y placement shift of the die bonder 100. Further, the bond head mount 103 and the z-axis motion table 106 include a linear guide which sustains a large upward force during bonding. This upward force passes through the bond head mount 103 and the z-axis motion table 106 and induces a placement shift on the bond head 101 and causes die tilting when performing bonding with a large bonding force. The operation is thus likely to bring about roll, pitch and yaw of the z-axis motion table 106, as well as to structurally deform the structure of the die bonder 100. All these deviations may serve to affect placement accuracy of the bond head 101. Therefore, this bond head design cannot achieve very high placement accuracy nor meet stringent requirements regarding non-tilting of the die 108.
Another prior art die bonder 100′ is shown in FIG. 2, which is a side view of a conventional die bonder incorporating a pneumatic cylinder 112 to provide a bonding force. A bond head 101′ is mounted to a bond force motor in the form of the pneumatic cylinder 112 coupled to a z-axis motion table 106 via a spherical point of contact 114. A large bonding force is applied with the aid of the pneumatic cylinder 112 mounted to a support structure 118. The large bonding force loading is sustained by the support structure 118 directly and the main lines of force bypass the bond head mount 103 and the z-axis motion table 106. Thus, deformation of the bond head mount 103 and the z-axis motion table 106 is avoided. Die tilting due to the bond head mount 103 and deformation of the z-axis motion table 106 structure can also be avoided. Placement error due to the roll, pitch and yaw of the z-axis motion table 106 can also be reduced as there is no z-axis drive-in motion by the z-axis motion table 106. However in this design, the bond head 101′ does not exhibit theta motion as it is fixedly coupled to the pneumatic bond force actuator, which is solely a linear driver. Hence, there is no rotary or theta compensation before the picked die 108 is bonded.
It would be desirable to implement a bond head capable of generating a large bonding force with reduced placement error, as well as provide rotary or theta compensation to correct any rotary offset of the die.